Apparatus for laser treatment of body lumens

ABSTRACT

A laser microsurgical method and apparatus are disclosed for safely treating occluded body lumens with laser energy. The disclosed method involves the use of pulsed laser energy from an argon-ion laser to destroy the tissue of luminal occlusions, such as atheromatous plaque and the like, with substantially no thermal necrosis of the surrounding tissue. A flexible catheter and associated laser microsurgical system is also disclosed which provides for aiming of the fibers to transmit the laser beam at the distal end of the catheter and rotational positioning of the catheter to permit coverage of virtually the entire cross-sectional area of the lumen. A lens system at the distal end of each laser fiber minimizes beam divergence and directs the beam toward the central axis of the catheter. A further embodiment of the catheter of the invention provides an array of laser fibers which are optically scanned with laser energy to cover the cross-sectional area of the lumen. The system is designed to minimize the possibility of damage to or perforation of the surrounding tissue of the lumen.

This application is a continuation of U.S. patent application Ser. No.772,677 filed Sept. 5, 1985 now U.S. Pat. No. 4,784,132 which is acontinuation-in-part of U.S. patent application Ser. No. 478,781, filedMar. 25, 1983, now U.S Pat. No. 4,800,876, which is acontinuation-in-part of U.S. Patent Application Serial No. 329,978,filed Dec. 11, 1981, now abandoned, which is a continuation of U.S.patent application Ser. No. 087,894, filed Oct. 24, 1979, now abandoned,which is a continuation-in-part of U.S. patent application Ser. No.032,844, filed Apr. 24, 1979, now abandoned. BACKGROUND OF THE INVENTION

The present invention relates to a method of and apparatus for the lasertreatment of occluded body lumens of mammals, especially humans, andmore particularly to the intraluminal use of laser energy to perforateand/or remove luminal occlusions, such as thrombi and/or atheroscleroticplacques in the cardiovascular system.

Cardiovascular disease is a major cause of death and morbidity andmanifests a grave concern to both the scientific community and the laypublic. Arteriosclerotic cardiovascular pathophysiology is a complex ofdiseases which affects many blood vessels in the body, the decreasedlumen diameter causing tissue ischemia. Other very common diseases, suchas diabetes mellitus, enhance the occlusion of important blood vesselsand ischemia of the organs they supply. Those diseases, aggravated bysuch other common abnormalities as hypertension, and other vasculardiseases and cardiovascular diseases, account for cerebrovascularaccidents, myocardial infarctions, and other devastating illnesses,including loss of life and limb. Unfortunate individuals affected witharteriosclerotic cardiovascular disease and the related vasculopathiesoften manifest disease in coronary, carotid and cerebral arteries, inpopliteal, tibial and dorsalis pedis arteries of the lower extremitiesand in other vessels. Those individuals, apart from having a shortenedlife expectancy, and suffering from sudden death, frequently also sufferfrom other debilitating problems including angina, shortness of breathand restricted activity, claudication or restricted use of the lowerextremities, sometimes with loss of those extremities from disease, andloss of functions of movement, speech, cerebral interpretation andcognitive abilities.

Historically, there are few effective means for preventing some of theforegoing disastrous medical problems. Patients with certain types ofcoronary insufficiencies documented by certain coronary angiographicfindings may be helped symptomatically by coronary artery bypassoperations. Other patients sometimes may be benefited by other types ofarterial surgery, for example, various bypass operations, orendarterectomies, which surgically attempt recanalization of certainoccluded blood vessels or other operations. Those are generally patientswith severe disease, but yet who meet certain diagnostic criteria andwho are healthy enough to undergo what amounts to major surgery withrelatively high morbidity and mortality rates. The cost is immense formany of these operations and incumbent hospitalization, includingexpensive special equipment which is required, and special trainingwhich is necessary for a team to operate the special surgical equipment.For example, it is estimated that a single coronary bypass operation maycost a patient over $50,000 including the hospitalization fees, andsurgical fees. Availability of this special type of surgery for vascularproblems is limited. Long term efficacy of coronary bypass surgery is asyet unknown, and the appropriate diagnostic and surgical criteria remaincontroversial. Because of the severity of the morphology and nature ofthe disease, for many patients treatment has been unavailable and hasbeen beyond the current scope of surgical intervention. For example,many patients lose extremities or their lives by virtue of having theseinoperable conditions.

In a different context, problems of lumens of the body, particularlysmall lumens, are complicated by occlusive diseases of other types. Asan example in the nervous system, the Aqueduct of Sylvius, in theventricular system of the brain, may be blocked in a child born withcongenital hydrocephalus. This condition necessitates a complicated andoften unsuccessful corrective neurosurgical procedure known as shunting.Considering the genito-urinary system, for example, fallopian tubes maybecome occluded by inflammatory or other disease processes. This maycause infertility and is a common problem. There is no effectivetreatment for this problem at this point in time, and this hasstimulated interest in the "test tube baby" controversy.

One suggested solution to the problem of atherosclerotic obstructions isa non-operative technique to improve coronary blood flow known aspercutaneous transluminal coronary angioplasty (PTCA). Generally, PTCAinvolves introducing a balloon catheter into the femoral artery or bybrachial cutdown and fluorscopic positioning at the appropriate coronaryostium. Pressure monitoring is also used to aid in positioning theballoon tip of the catheter at the stenosis. The balloon is inflated for3-5 seconds to mechanically enlarge the stenosis and is then deflatedfor measurement of distal coronary pressure. The cycle may be repeatedseveral times until a satisfactory decrease in pressure gradient isachieved.

Although the PTCA technique is sometimes effective to improve coronaryblood flow, there are complications which must be weighed beforeundertaking the procedure. Such complications which may occur includearterial spasms, myocardial infarction, thrombotic occlusion,embolization and dissection, or frank perforation of the vessel wall.

It has also been suggested that cardiovascular occlusions, as well asocclusions in other body lumens, might be vaporized by means ofcontinuous wave (CW) laser energy. U.S. Pat. No. 4,207,874 to Choy, forexample, discloses a flexible conduit which accommodates a fiberopticbundle divided into light source, viewing and laser bundle portions. Theflexible conduit is introduced into a vein or other body lumen andadvanced until it contacts an obstruction such as a thrombus. A laserapparatus optically associated with the laser fiber bundle is thenactivated so that the laser energy vaporizes the obstruction, theremaining particles of which are then removed by suction.

Other flexible laser endoscopes for use in the therapeutic lasertreatment of body lumens are disclosed in U.S. Pat. Nos. 4,072,147;4,146,019; 4,170,997; and German Offenlegungsschrift No. 2,640,406. Suchintraluminal laser devices typically are said to function by thermalvaporization and/or coagulation of the luminal obstruction mass.

One of the most serious risks inherent in the intraluminal use of laserradiation, especially in coronary or cerebral blood vessels, is thepossibility of perforation of or thermal damage to the vessel walls andsurrounding tissue. Accordingly, intravascular recanalization ofoccluded blood vessels is still an experimental procedure.

Recently, investigators have reported the use of continuous wave (CW)argon, neodymium-YAG and carbon dioxide laser sources to successfullyvaporize, coagulate and penetrate atherosclerotic placque in animals andin sections of coronary arteries taken from human cadavers. However, theinvestigators also report perforation of the vessel walls in many cases,particularly at laser energy levels which have been increased to a levelsufficient to effect vaporization of the placque.

Such laser energy levels are appropriately characterized as the"thermal" mode of laser operation which involves causing damage totissue by virtue of heat accumulation in the tissue impinged by thelaser radiation. Excessive heat accumulation causes thermal degradationor thermal necrosis. In other words, the temperature of the tissuerises, tissue proteins are denatured and ultimately the tissue iscoagulated and "evaporated" or "vaporized." While the laser thermalenergy mode is effective in coagulating and vaporizing many tissues,including the tissues forming atherosclerotic placques and stenoses, itsuse heretofore in occluded coronary and cerebral blood vessels, forexample, is not sufficiently safe and controllable. Consequently, theproblem of inadvertent damage to or destruction of surrounding vesseltissue has been a major obstacle in the development of an acceptablemicrosurgical technique for laser angioplasty in the human vascularsystem.

Apart from the risk of using continuous wave (CW) laser energy in thehuman vascular system, the prior art intraluminal laser devices lackeffective mechanisms for "aiming" the laser beam to minimize thepossibility of inadvertent damage to the vessel walls and to maximizethe exposure of a large area of the occlusion, e.g., the atheroscleroticplacque, to the laser energy.

SUMMARY AND OBJECTS OF THE INVENTION

In view of the foregoing limitations and shortcomings of the prior artintraluminal laser devices, as well as other disadvantages notspecifically mentioned above, it should be apparent that there stillexists a need in the art for a laser microsurgical apparatus for use incoronary angioplasty which is capable of effecting recanalization ofoccluded coronary and cerebral blood vessels at minimum risk ofperforation or thermal necrosis of the vessel walls. It is, therefore, aprimary objective of this invention to fulfill that need by providing anovel coronary arterial catheter and associated laser microsurgicalsystem and a method of using the same whereby the laser energy radiatedwithin the cardiovascular system is carefully controlled and aimed insuch a way as to effectively destroy or penetrate atheroscleroticplacque, yet minimize the risk of vascular perforation or thermalnecrosis of the surrounding tissue.

More particularly, it is an object of the present invention to providean effective method of delivering laser energy in a safe, substantiallynon-heat conducting or conduction-free mode by controlling the pulsewidth or duration, pulse repetition rate, and duty cycle of the laserenergy within predetermined ranges and by using optical switching tosequentially direct the laser energy at selected target areas.

It is another object of the present invention to provide a flexiblecatheter adapted to be inserted into a body lumen, such as an obstructedcoronary artery, said catheter having one or more quartz glass laserfibers which can be "aimed" at a particular target within a target areacomprising substantially the entire cross-sectional area of the bodylumen.

Yet another object of the invention is to provide a laser microsurgicalsystem connected to the proximal end of a flexible angiographic catheterfor controlling the positioning, illumination, visualization, firing andanalysis functions of the system.

Still another object of the invention is to provide a flexibleangiographic catheter for use in occluded blood vessels in combinationwith laser microsurgical apparatus, said catheter having one or morelaser fibers, each of which is provided with a lens system whichminimizes divergence of the laser beam and prismatically cants the laserbeam toward the center of the blood vessel to intensify the cuttingeffect of the beam and to minimize the possibility of perforation of thevessel walls.

Another object of the invention is to provide a flexible catheteradapted to be inserted into a body lumen and having a plurality of laserfibers disposed within the catheter, such fibers being selectivelyscanned with laser energy by an optical scanner to "aim" the laserenergy at a particular target area in the overall cross-sectional areaof the body lumen.

Briefly described, the aforementioned objects of the invention areaccomplished according to its apparatus aspects by providing a flexiblecatheter having an outside diameter from about 1.2 to about 5.0millimeters, which is especially suitable for use in coronary, cerebraland somewhat larger carotid blood vessels, for example, to removeocclusions, such as atheromatous placque. Within the catheter sheaththere are provided a plurality of optical fibers and fluid channels.

In one embodiment of the invention, the optical fibers include a bundleof laser transmitting fibers eccentrically arranged relative to thecatheter axis and radially movable toward that axis by means of aballoon positioned within the catheter sheath. Each laser fiber has adistal lens system which converges and cants the radiation beam awayfrom the circumference of the catheter and toward the axis thereof.Alternate embodiments of the catheter include distal lens systems forthe laser fibers which may comprise one or more diverging lenses forspecial applications or techniques to be hereinafter described.

A flexible optical fiber viewing element with a distal lens system isprovided within the catheter sheath which comprises a plurality ofindividual fibers having a glass cladding and extending over asubstantial part of the cross-sectional area of the catheter, forinstance, 50% or more. An illuminating system comprising severalindividual plastic clad quartz glass fibers cooperates with the opticalviewing element and is arranged adjacent thereto for delivering whitelight from a conventional light source.

Fluid systems within the catheter include an outflow or suction channelfor removal of fluids and debris and two or more inflow channels forinjection of saline, pharmacologic agents, radiopaque positioning dyes,immuno-specific antibodies and the like. Carbon dioxide gas channels arealso provided for inflation/deflation of both the laser aiming balloonand a balloon circumferentially disposed about the catheter adjacent thedistal end thereof for occluding the vascular lumen and for establishingstabilization of the catheter distal end relative to said lumen.

A laser microsurgical system is operatively connected to the proximalend of the flexible angiographic catheter and comprises a proximaloptical and fluid coupler for interconnecting the optical fibers andfluid channels of the catheter to the various system components, such asthe laser apparatus and control, laser fiber optical scanner,illumination and visualization systems, positioning systems and fluidsystems.

The objects of the invention are accomplished according to its methodaspects by the use of visible light laser energy in the wavelength rangeof 351 to 515 nanometers, and, preferably, the blue-green emission linesat wavelengths of 488 and 514 nanometers from an argon-ion laser with apeak power output of about 20 watts, such as a Spectra-Physics 171Laser. The argon laser apparatus is operated in the pulsed ornon-conducting mode using a pulse width or duration in the range of from5 to 200 milliseconds and a pulse repetition rate of 1 to 50 pulses persecond with a duty cycle of between 5 and 50%. The preferred pulseenergy is in the range of from 150 to 500 millijoules. Spot size foreach fiber in the laser fiber bundle may be from 100 to 500 microns,preferably, the largest possible spot size in that range compatible withenergy density requirements.

The above parameters of the pulsed laser energy are selected to effectdamage to a luminal obstruction with substantially no thermal necrosisof the surrounding tissue. A hole is drilled in the obstruction byheating a given volume of the tissue thereof to its boiling point andthen supplying the heat of vaporization to that volume to convert it tovapor. Ideally, the total laser energy needed to vaporize the givenvolume of the tissue of the obstruction is delivered in such a shortperiod of time that heat conduction to the surrounding tissue isnegligible. That time period is defined as the "thermal time constant"or "thermal relaxation time" for the given volume of tissue. Accordingto the invention, the pulse characteristics, e.g., pulse width, pulserepetition rate and energy, are selected to operate in theconduction-free mode, that is, the laser energy is preferably deliveredjust at the threshold of the thermal relaxation time of the illuminatedvolume of the obstruction tissue.

Experimental results have indicated that over the range of laser focaldiameters of 50 to 100 microns for an argon-ion laser, the diameter ofthe laser drilled hole in arterial placque is approximately 500 microns,i.e., 5 to 10 times greater than the laser focal diameter. Thatphenomenon is believed to be the result of a combination of strong,small angle scattering and weak absorption of the placque tissue. Thelarger area, and consequent larger volume, of illuminated tissue resultsin a greater energy threshold for drilling the placque, that is, agreater thermal input is necessary because of the scattering of thelaser light and the absorption characteristics of the placque. For theargon-ion laser, the energy threshold is about 200 millijoules per pulseover a pulse width of 200 milliseconds or less.

An alternate embodiment of the invention takes advantage of theforegoing experimental results by locating a plurality of laser fibersin a flexible catheter in an array with the laser fibers appropriatelyspaced to provide substantially complete coverage of the cross-sectionalarea of a body lumen or vessel with little or no overlapping of thedrilled laser hole. Thus, "aiming" may be accomplished by opticallyscanning the plurality of laser fibers to impinge laser energy onselected target areas, e.g., a plurality of target areas, each having a500 micron diameter, over the entire cross-sectional area confrontingthe distal end of the catheter. Optical scanning of the laser fibers ina predetermined sequence also permits a greater number of pulses or"shots" to be made in a given time period without exceeding the energythreshold and causing thermal necrosis of the surrounding tissue. Thelaser fibers disposed adjacent the outermost periphery of the cathetermay also be "skewed" toward the center of the catheter to minimize thepossibility of perforation of the luminal wall.

With the foregoing and other objects, advantages and features of theinvention that will become hereinafter apparent, the nature of theinvention may be more clearly understood by reference to the followingdetailed description of the invention, the appended claims, and to theseveral views illustrated in the attached drawings

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transverse cross-sectional view of a first embodiment of theflexible catheter of the present invention taken along line 1--1 of FIG.2;

FIG. 2 is a longitudinal cross-sectional view, partly broken, of thefirst embodiment of the catheter of the invention taken along line 2--2of FIG. 1;

FIGS. 3A-3D are transverse cross-sectional views similar to FIG. 1showing the positioning of the laser fiber bundle;

FIG. 4 is a view illustrating the positioning of the distal end of thecatheter in a body lumen adjacent a partial occlusion of the lumen;

FIG. 5 is a schematic block diagram showing the laser microsurgicalsystem of the present invention;

FIG. 6 is a transverse cross-sectional view of the distal end of analternate embodiment of the flexible catheter of the present invention,taken along line 7--7 of FIG. 6; and

FIG. 7 is a longitudinal cross-sectional view of the catheter of FIG. 6taken along line 7--7 showing skewing of the outermost laser fibers.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now in detail to the drawings wherein the same parts aredesignated by the same reference numerals throughout, there isillustrated in FIGS. 1 and 2 cross-sectional details of the distal endof the inventive flexible catheter which is designated generally byreference numeral 10. In those circumstances wherein a particularelement or aspect of the invention has been described in greater detailin one or more of the aforementioned copending related applications,appropriate reference will be made herein to such application(s).

The catheter 10 comprises a plastic sheath 12 which may be a non-toxicpolyvinylchloride (PVC) or other suitable non-toxic plastic material.The outside diameter of the catheter 10 for use in the laser coronaryangioplasty techniques described herein is from about 1.2 to about 5.0millimeters, but may be larger in diameter for use in other, larger bodylumens.

Disposed within the catheter sheath about the central axis 14 thereofare a plurality of elements extending longitudinally of the catheterand, for convenience of illustration, are shown in FIGS. 1 and 3A-3D asbeing somewhat loosely disposed in spaced relation to one another. Inthe actual construction of the catheter, the elements are in closerproximity to one another than shown in the drawings to provide asomewhat greater packing density consistent with the requirement forshifting the laser fiber bundle relative to the catheter axis in themanner described hereinafter.

A laser fiber bundle 16 is arranged eccentrically of the catheter axis14 and, in a preferred form, comprises four quartz glass laser fibers18a-18d for transmitting the laser energy, each fiber having a corediameter of from 50 to 200 microns. Laser fibers 18a-18d are embedded ina laminated sheath or cladding 20 of non-toxic polyethylene or PVC. Asshown in FIG. 1, the four laser fibers are preferably orthogonallyarranged with the axes of two of the fibers 18a and 18c disposed on aradial plane through the catheter axis 14.

An elongate balloon 22 is bonded or otherwise affixed to thecircumference of the laser fiber bundle 16 at the portion thereofproximate the catheter sheath 12 and extends parallel to the axis of thelaser fiber bundle as shown in FIG. 2. Inflation of the balloon 22exerts a radially inward force on the laser bundle 16 tending to urgethe same toward the catheter axis 14 and thereby "aiming" the laserenergy as more fully described hereinafter in connection with FIGS.3A-3D.

Arranged at the lowermost portion of the catheter, as viewed in FIG. 1,is a visualization optical element 24 which is of generally conventionalconstruction. Optical viewing element 24 is generally crescent-shaped incross-section and comprises a plurality of 5,000 to 10,000 individualglass fibers 26, each having a hexagonal cross-section to improve thepacking factor The fibers 26 each have a flat-to-flat dimension of about4 microns and are packed tightly together and fused only at theirproximal and distal ends to preserve flexibility. The bundle of fibersis ensheathed in a glass cladding 28 and a lens system 30 (FIG. 2) ofknown configuration, i.e., two plano-convex lenses, is fused to thedistal end of the viewing element 24 for providing wide anglevisualization within the body lumen. See also related U.S. patentapplication Ser. No. 329,978.

Illumination of the surgical area is provided by three fused quartzglass fibers 32, 34, 36 of about 50 microns diameter which are clad witha PVC sheath 38 As shown in FIG. 1, the illuminating fibers arepreferably arranged substantially diametrically for most effectiveillumination of the central portion of the body lumen.

The fluid systems of the catheter, in addition to the laser fiber aimingballoon 22, include a suction channel 40 and two inflow channels 42, 44.The suction channel 40 is used for debris removal and for suctioningfluids from the intraluminal region at the distal end of the catheterInflow channels 42, 44 are employed for injecting fluids such as saline,pharmacologic agents, radiopaque positioning dyes and immuno-specificantibodies, among others.

A conventional circumferential balloon 43 is arranged about the catheter10 adjacent the distal end thereof as shown in FIG. 4. Inflation ofballoon 43 occludes flow in the lumen L and establishes a fixed,stabilized position of the distal end of the catheter 10. Such balloonsand the methods and apparatus for inflating and deflating the same arewell-known in the art and, therefore, need not be described in greaterdetail herein.

As shown in FIG. 2, at the distal end of each laser fiber 18a-18d, thereis epoxied a converging lens 46 for focusing the laser energy beam andpreventing undesirable divergence toward the luminal wall and a prism 48for bending or "canting" the eccentric laser beam from each fiber towardthe center of the lumen. Total divergence angle of the preferred 100-500micron diameter spot for each fiber is preferably no greater than 5°.Preferably, the optical axes of the prismatically canted laser beams aremaintained in parallel relationship to prevent spot "overlap" and beamdivergence.

In certain circumstances, it may be desirable to insert a catheter witha laser fiber bundle having a diverging lens system at the end of eachlaser fiber. For instance, if the distal end of the catheter directlyabuts an occlusion of atheromatous placque, a greater laser impact areacould be achieved with a diverging lens arrangement. After destructionof the first few millimeters of the placque is accomplished the catheterwould normally be replaced by a catheter having the converging lenssystem shown in FIG. 2

With reference now to FIGS. 3A-3D, FIG. 3A corresponds substantially toFIG. 1 and shows the balloon 22 in its deflated condition with the laserfiber bundle in its most eccentric radial position in relation to thecentral axis 14 of the catheter. As the balloon 22 is graduallyinflated, the laser fiber bundle is incrementally urged substantiallyradially toward the axis 14 until it reaches a position of minimumeccentricity as shown in FIG. 3B.

FIGS. 3C and 3D illustrate the same conditions of inflation/deflation ofballoon 22 as shown in FIGS. 3A and 3B, respectively, except that thecatheter 10 has been rotated exactly 180°. It will be understood bythose skilled in the art that by the appropriate selection of angle ofrotation of the catheter and incremental inflation/deflation of balloon22, the four 200 micron spots from the laser fibers 18a-18d can bepositioned to impinge at any target area over virtually the entirecross-sectional area of the body lumen being treated.

Referring now to FIG. 4, the distal end of the catheter 10 is shownfixed in position in a lumen L adjacent a partial occlusion X. Theuppermost pair of diverging dotted lines represents a laser energy beamB from laser fiber 18a when said fiber is positioned on a vertical planeat a location of greatest eccentricity from the catheter axis. Beam Bhas a total divergence angle 50 of 5°; however, because the beam hasbeen prismatically canted by the lens system 46, 48 shown in FIG. 2, thediverging beam does not impinge on the wall of the lumen L, but ratheris directed toward the central portion of the lumen L. Likewise, thelowermost pair of diverging dotted lines in FIG. 4 represents a laserenergy beam B' from laser fiber 18a when said fiber is positionedexactly 180° from the position at which beam B was generated. Beam B'also has a total divergence angle 52 of 5° as shown in FIG. 4.

It should be apparent from the foregoing description of FIGS. 3A-3D andFIG. 4 that the laser energy beams transmitted by the laser fiber bundle16 of the catheter are not only capable of being "aimed" at virtuallyany target area within the lumen, but are converged and canted so as tominimize the possibility of laser beam impingement on the lumen walls.

Positioning of the distal end of the catheter 10 is aided by knownradiographic visualization procedures. For this purpose, it isadvantageous to mark the periphery of the distal end of the catheterwith a plurality of radiopaque strips 54, 56, 58 of predetermined sizeand positioned for determining both the rotational and axial positionsof the catheter within a coronary artery, for example

The laser microsurgical system 60 of the invention is shownschematically in FIG. 5 The system 60 includes a laser source 62 whichis preferably an argon-ion laser, such as a Spectra-Physics 171 Laserfor generating a pulsed laser beam. The output of laser source 62 is apulsed laser beam 64 which is inputted to a multi-fiber optical scanner66 of a known type, for example, of the type described by Fujii et al inApplied Optics, Vol. 21, No. 19, pp. 3437-3442, Oct. 1, 1982. Scanner 66is used to scan the four laser fibers 18a-18d of the laser fiber bundle16 with pulsed laser beam 64.

Control of pulse width or duration, pulse repetition rate, wavelength,length of exposure, intensity and firing is provided by a laser control68 associated with the laser source 62. Firing of the laser 62 isaccomplished by closing a firing switch 69 which may be, for example, afoot pedal switch

The proximal end of the optical visualization element 24 supplies anoptical image to a viewing microscope 70 which has a built-in eyepieceshutter mechanism 72. The shutter 72 is responsive to activation of thelaser source 62 to prevent back-scatter of laser energy which coulddamage the surgeon's eyes.

The optical image from optical element 24 is also supplied to an imageanalyzer 74 controlled by microprocessor 76 both of which are used toanalyze the visual images transmitted from the intraluminal region atthe distal end of the catheter and to aid in longitudinal positioning ofthe catheter distal end, "aiming" of the laser fiber or fibers at theappropriate target in the intraluminal region and timing of the laserfiring signal in relation to the cardiac cycle. A suitablemicroprocessor and image analyzer is a Videoplan Computerized ImageAnalyzer available from Carl Zeiss, Inc., 444 Fifth Avenue, New York,New York 10018.

A conventional cathode ray tube video display 78 and video recorder 80are connected to the image analyzer for real time observation andrecording, if desired, of the microsurgical procedure.

An illumination source 82 is connected to the proximal ends of opticalfibers 32, 34, 36 for delivery of white light thereto. The light isprovided by mercury or xenon high pressure arc lamps within quartzenclosures; however, other types of light sources may be used. A vacuumunit 84 and fluids input unit 86 are connected to the suction channel 40and fluid inflow lines 42, 44, respectively

For inflation and deflation of the aiming balloon 22 and circumferentialballoon 43, a fluid pressure source 88, such as pressurized carbondioxide, is connected through respective electrically-operable solenoidvalves 90, 92 to the pneumatic tubes 94, 96 supplying the aiming balloon22 and the circumferential balloon 43, respectively

The proximal end of the catheter 10 is mounted in an axial androtational drive mechanism 98 which rotates the catheter about its axisand moves the same axially in response to mechanical or electricalsignals from a micromanipulator 100 which, in turn, receives commandsignals from the microprocessor 76. Suitable micropositioners arewell-known in the art and are available from numerous sources, such asKlinger Scientific Corporation, 110-120 Jamaica Avenue, Richmond Hill,New York 11148. See also related application, Ser. No. 329,978.

It is also advantageous to synchronize the occlusion of the coronaryartery with the balloon 43 and the firing of the laser 62 with thecardiac cycle. Generally, it is desirable to inflate the catheterballoon 43 during the filling phase of the cardiac cycle and deflate theballoon during the pumping phase of the cardiac cycle. In that way,blood flow is occluded under minimal pressure conditions in the coronaryartery. For this purpose, a conventional counterpulsator 102 may be usedwhich senses ventricular output with an aortic catheter independently ofthe catheter 10 of the invention. One suitable counterpulsator is knownas System 82 and is manufactured by Datascope Corporation, 580 WintersAvenue, Paramus, New Jersey 07652. See also related application, Ser.No. 329,978.

An alternative or second embodiment of the catheter of the invention isshown in FIG. 6 and identified with reference numeral 110. The catheter110 comprises a plastic sheath 112 similar to the sheath 12 of the FIG.1 or first embodiment of the invention, the outside diameter of which ispreferably from about 1.2 to about 5.0 millimeters for use in thedescribed laser coronary angioplasty techniques. The FIG. 6 embodimentillustrates a catheter having an outside diameter of about 1.5millileters which diameter is essentially defined by the arrangement ofthe laser fiber array disposed within the sheath 112 as explained ingreater detail hereinafter.

A plurality of elements similar to those illustrated in FIGS. 1 and 2are arranged to extend longitudinally within the sheath 112 about thelongitudinal axis 114 thereof and, like the showing of FIG. 1, aresomewhat loosely disposed in relation to one another, although in actualpractice the elements are packed in closer proximity, preferably in afixed relationship to one another and to the sheath 112.

The catheter 110 has a similar arrangement of optical viewing element124, illumination fibers 132, 134, 136, suction channel 140 and inflowchannels 142, 144 as the first embodiment of the invention. However, incontrast to the laser fiber bundle 16 of the first embodiment of theinvention, individually clad laser fibers 118 of the second embodimentare disposed about the catheter axis 114 in a predetermined, parallelarray designed to provide impingement of laser energy on substantiallythe entire cross-sectional area of an obstruction confronted by thecatheter 110 with little or no overlapping of laser impingement.

Inasmuch as experiments have indicated that drilled holes with anargon-ion laser have a diameter of about 500 microns regardless of laserfocal diameter, an array of seven (7) 50 to 200 micron diameter fibers118 in the arrangement shown in FIG. 6 will provide laser energycoverage of virtually the entire cross-sectional area of a luminalobstruction confronting the catheter 110, particularly in the centralregion thereof as shown by the dashed line areas 116 of laserimpingement. Advantageously, the largest areas 120 not included in thetotal laser impingement area are located at the outermost periphery ofthe catheter adjacent the vessel walls where laser energy impingement isleast desirable, and, in fact, may be detrimental.

In view of the above teachings, various arrangements of laser fibers fordifferent diameter catheters will be apparent to those skilled in theart. For example, the same seven (7) fiber array may be used for a 1.2millimeter diameter catheter by arranging the centers of the laserfibers at a 400 micron spacing rather than the 500 micron spacing shownin FIG. 6. While a certain amount of laser impingement overlap willresult from that arrangement, by appropriate scanning of the laserfibers with laser energy any overheating of the tissue can be avoided.

Generally speaking, a laser fiber disposed on the axis 114 of thecatheter is preferred, but is not essential. Thus, although a 1.2millimeter diameter catheter is preferably provided with an array of 5to 7 laser fibers, an array of four (4) laser fibers equiangularlyspaced may be provided with their impingement areas in targentialrelationship. While such an arrangement would not provide laserimpingement in the central region of an obstruction confronting thecatheter, destruction of the obstruction surrounding the central regionwill eliminate support of such central region and ultimately cause it togravitate to a laser impingement area where it will be destroyed.

In larger diameter catheters, a larger number of laser fibers arepreferably employed. For instance, a 5.0 millimeter diameter catheterencompasses an area 100 times greater than the 500 micron diameter areaimpinged by a single laser fiber. Therefore, an array of 80 to 100 laserfibers would be required to cover the entire area confronted by a 5.0millimeter diameter catheter.

The laser microsurgical system 60 shown schematically in FIG. 5 may alsobe used with the second embodiment of the catheter 110 of the inventionshown in FIG. 6. Advantageously, the multi-fiber optical scanner 66 maybe programmed to scan each of the laser fibers 118 with pulsed laserenergy in a preselected sequence. The scanning sequence is preferablyselected to operate in the conduction-free or non-heat conducting mode.In that way, the possibility of overheating and the consequent thermalnecrosis of a given impingement area is avoided, while at the same timethe number of pulses of laser energy that can be delivered to theimpingement area in a given time period is maximized.

Although the laser fibers 118 of the second embodiment of the inventionare described above as extending parallel to the catheter axis 114, asshown in FIG. 7, the distal ends of the outermost laser fibers may alsobe inclined or skewed inwardly toward the catheter axis by an angularamount identified by reference numeral 122. The amount of skewing mayamount to between 5° and 45°. Preferably, the distal ends of the laserfibers 118 are inserted or molded into an end plate 126 fixed to thesheath 112. The end plate 126 may also receive the other longitudinallyextending elements of the catheter, such as the viewing element 124,illumination fibers 132, 134, 136 and fluid channels 140, 142, 144.

The above-described skewing of the peripheral laser fibersadvantageously causes the outermost laser energy beams to convergetoward the axis of the body lumen or vessel and thereby provide furtherprotection against the possibility of perforation of the luminal wall.Such skewing, however, reduces the total area of laser illumination of agiven diameter of catheter and arrangement of laser fibers and resultsin varying degrees of laser beam overlap depending on the distancebetween the obstruction and the distal end of the catheter.

It would be possible to skew the distal ends of some of the interiorlydisposed laser fibers of an array having fiber groups disposed atvarying radial distances from the axis of the catheter. Such skewing maycause the axes of the fibers to diverge or converge with the catheteraxis so as to achieve overlapping of laser impingement if desired or to"aim" at areas not impinged by the laser beam or blind spots caused bythe positioning of other elements in the catheter, such as the elements124, 132, 134, 136, 142, 144, etc.

According to the method of the present invention, laser energy is notsupplied as continuous wave (CW) laser energy in the thermal mode tovaporize atheromatous occlusions as in the prior art, but rather aspulses of 5-200 millisecond duration at a pulse repetition rate of 1-50pulses per second and a duty cycle of between 5 and 50%. The pulseenergy is from 150 to 500 millijoules. The laser source 62 is anargonion laser delivering 20 watts peak power at wavelengths of about488 and 514 nanometers and a preferred spot size of about 100-500microns diameter. Pulsing of the laser source in the ranges describedabove has been advantageously found to be both safe and effective; safefrom the standpoint that the vessel walls will neither be perforated norsubjected to thermal necrosis, and effective from the standpoint thatthe laser energy is sufficiently great to effect vaporization of theocclusion.

The selection of specific values for the pulse duration, pulserepetition rate, pulse energy parameters within the aforesaid ranges toeffect destruction of an occlusion without thermal necrosis is dependentto a large extent on the thermal time constant and absorptioncharacteristics of particular type or material of the occlusion, e.g.,fibrin, cholesterol, calcium, collagen, low-density lipoproteins and thelike. Based on the teachings herein, however, one skilled in the art canreadily select a suitable value for each pulse parameter to effectconduction-free operation, i.e., destruction of the tissue of theocclusion with substantially no thermal necrosis of the surroundingtissue.

Although only preferred embodiments are specifically illustrated anddescribed herein, it will be appreciated that many modifications andvariations of the present invention are possible in light of the aboveteachings and within the purview of the appended claims withoutdeparting from the spirit and intended scope of the invention.

What we claim is:
 1. Apparatus for performing laser surgery in a bodylumen having an obstruction therein comprising:catheter means forinsertion in the body lumen, said catheter means having a longitudinalaxis and proximal and distal ends, fiber means arranged in said cathetermeans for transmitting a beam of laser energy from said proximal end tosaid distal end of said catheter means to impinge upon the obstructionin said body lumen; laser means arranged adjacent the proximal end ofsaid catheter means for generating a non-continuous wave, pulsed laserbeam having a predetermined pulse duration, pulse repetition rate, pulseenergy and duty cycle selected to effect damage to the obstruction withsubstantially no thermal necrosis of the surrounding tissue of the bodylumen.
 2. Apparatus according to claim 1, wherein said fiber meansinclude a plurality of optical fibers, said laser means comprises anoptical scanning means for scanning said fibers with said beam of laserenergy.
 3. Apparatus according to claim 2, wherein the distal ends ofsome of said fibers are converged radially inwardly at an angle towardsaid longitudinal axis.
 4. Apparatus according to claim 3, including anend plate disposed at the distal end of said catheter means for mountingthe distal ends of said fibers.
 5. Apparatus according to claim 2,wherein the distal ends of some of said fibers are diverged radiallyoutwardly at an angle away from said longitudinal axis.
 6. Apparatus forperforming laser surgery in a body lumen having an obstruction thereincomprising:catheter means for insertion in the body lumen, said cathetermeans having a sheath and a longitudinal axis and proximal and distalends, at least one fiber means arranged in said catheter means fortransmitting a beam of laser energy from said proximal end to saiddistal end to impinge upon the obstruction in said body lumen; lasermeans arranged adjacent the proximal end of said catheter means forgenerating a non-continuous wave, pulsed laser beam having apredetermined pulse duration, pulse repetition rate, pulse energy andduty cycle selected to effect damage to the obstruction withsubstantially no thermal necrosis of the surrounding tissue of the bodylumen; and aiming means arranged within the sheath of said cathetermeans for shifting the distal end of said fiber means relative to saidsheath and the longitudinal axis of the catheter means whereby saidlaser beam is selectively aimed to impinge upon different points on theobstruction.
 7. Apparatus according to claim 6, including means forrotating said catheter means about the longitudinal axis thereof. 8.Apparatus according to claim 6, wherein said aiming means comprises aballoon arranged in said catheter means adjacent said fiber means andmeans for incrementally inflating and deflating said balloon. 9.Apparatus according to claim 6, including a lens system disposed at thedistal end of said fiber means, said lens system comprising a converginglens converging said beam and a prism for canting said beam toward thelongitudinal axis of said catheter means.
 10. Apparatus according toclaim 8, wherein said fiber means is arranged eccentrically in saidcatheter means, said balloon being inflatable and deflatable to movesaid fiber means substantially radially of said catheter means. 11.Apparatus according to claim 6, including a source of laser energy, saidfiber means comprising a plurality of optical fibers, an optical scannermeans interposed between said laser energy source and the proximal endof said fiber means for scanning said fibers with said laser energy. 12.Apparatus according to claim 6, including a circumferential balloonarranged about the distal end of said catheter means and means forinflating and deflating said circumferential balloon in synchronism withthe cardiac cycle.
 13. Apparatus according to claim 6, furthercomprising:means for rotating said catheter about the longitudinal axisthereof; a lens system disposed at the distal end of said fiber means,said lens system comprising a converging lens for converging said laserbeam and a prism for canting said beam toward the longitudinal axisthereof; said fiber means being eccentrically arranged in said cathetermeans, said aiming means comprising a balloon arranged along said fibermeans; and means for inflating and deflating said balloon such that saidfiber means is shifted substantially radially of said catheter means.14. Apparatus for performing laser surgery in a body lumencomprising:catheter means for insertion in the body lumen, said cathetermeans having a sheath and a longitudinal axis and proximal and distalends, at least one fiber means arranged in said catheter means fortransmitting a beam of laser energy from said proximal end to saiddistal end to impinge upon an obstruction in the body lumen; means forrotating said cathetermeans about the longitudinal axis thereof; andaiming means arranged within the sheath of said catheter means forshifting the distal end of said fiber means relative to said sheath andthe longitudinal axis of the catheter means whereby said laser beam isselectively aimed to impinge upon different points on said obstructionwith substantially no movement of said catheter means relative to thebody lumen, said aiming means comprising a balloon arranged in saidcatheter means adjacent said fiber means and means for incrementallyinflating and deflating said balloon.
 15. Apparatus according to claim14, wherein said fiber means is arranged eccentrically in said cathetermeans, said balloon being inflatable and deflatable to move said fibermeans substantially radially of said catheter means.
 16. Apparatusaccording to claim 14, including a source of laser energy, said fibermeans comprising a plurality of optical fibers, an optical scanner meansinterposed between said laser energy source and the proximal end of saidfiber means for scanning said fibers with said laser energy. 17.Apparatus for performing laser surgery in a body lumencomprising:catheter means for insertion in the body lumen, said cathetermeans having a sheath and a longitudinal axis and proximal and distalends, at least one fiber means arranged in said catheter means fortransmitting a beam of laser energy from said proximal end to saiddistal end to impinge upon an obstruction in the body lumen; a lensmeans disposed at the distal end of said fiber means, said lens meanscomprising a converging lens for converging said beam and a prism forcanting said beam toward the longitudinal axis of said catheter means;and aiming means arranged within the sheath of said catheter means forshifting the distal end of said fiber means relative to said sheath andthe longitudinal axis of the catheter means whereby said laser beam isselectively aimed to impinge upon different points on said obstructionwith substantially no movement of said catheter means relative to thebody lumen.
 18. Apparatus for performing laser surgery in a body lumencomprising:catheter means for insertion in the body lumen, said cathetermeans having a sheath and a longitudinal axis and proximal and distalends, at least one fiber means arranged eccentrically in said cathetermeans for transmitting a beam of laser energy from said proximal end tosaid distal end to impinge upon an obstruction in the body lumen; meansfor rotating said catheter about the longitudinal axis thereof; a lenssystem disposed at the distal end of said fiber means, said lens systemcomprising a converging lens for converging said laser beam and a prismfor canting said beam toward the longitudinal axis thereof; aiming meanscomprising a balloon arranged within the sheath of said catheter meansfor shifting the distal end of said fiber means relative to said sheathand the longitudinal axis of the catheter means; and means for inflatingand deflating said balloon such that said fiber means is shiftedsubstantially radially of said catheter means whereby said laser beam isselectively aimed to impinge upon different points on said obstructionwith substantially no movement of said catheter means relative to thebody lumen.
 19. Apparatus for performing laser angioplasty by effectingdamage to an obstruction in the vascular system of a human comprising:alaser means for generating a non-continuous wave, pulsed laser beamhaving a predetermined pulse duration, pulse repetition rate, pulseenergy and duty cycle selected to operate substantially at the thresholdof the thermal relaxation time of the irradiated volume of theobstruction such that damage is effected to the obstruction withsubstantially no thermal necrosis of the surrounding tissue of thevascular system; and a flexible optical fiber means for transmittingsaid laser beam from said laser means through the vascular system to theobstruction therein.